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SUBROUTINE slAOPA ( DATE, DUT, ELONGM, PHIM, HM,
: XP, YP, TDK, PMB, RH, WL, TLR, AOPRMS )
*+
* - - - - - -
* A O P A
* - - - - - -
*
* Precompute apparent to observed place parameters required by
* slAOPQ and slOAPQ.
*
* Given:
* DATE d UTC date/time (modified Julian Date, JD-2400000.5)
* DUT d delta UT: UT1-UTC (UTC seconds)
* ELONGM d mean longitude of the observer (radians, east +ve)
* PHIM d mean geodetic latitude of the observer (radians)
* HM d observer's height above sea level (metres)
* XP d polar motion x-coordinate (radians)
* YP d polar motion y-coordinate (radians)
* TDK d local ambient temperature (K; std=273.15D0)
* PMB d local atmospheric pressure (mb; std=1013.25D0)
* RH d local relative humidity (in the range 0D0-1D0)
* WL d effective wavelength (micron, e.g. 0.55D0)
* TLR d tropospheric lapse rate (K/metre, e.g. 0.0065D0)
*
* Returned:
* AOPRMS d(14) star-independent apparent-to-observed parameters:
*
* (1) geodetic latitude (radians)
* (2,3) sine and cosine of geodetic latitude
* (4) magnitude of diurnal aberration vector
* (5) height (HM)
* (6) ambient temperature (TDK)
* (7) pressure (PMB)
* (8) relative humidity (RH)
* (9) wavelength (WL)
* (10) lapse rate (TLR)
* (11,12) refraction constants A and B (radians)
* (13) longitude + eqn of equinoxes + sidereal DUT (radians)
* (14) local apparent sidereal time (radians)
*
* Notes:
*
* 1) It is advisable to take great care with units, as even
* unlikely values of the input parameters are accepted and
* processed in accordance with the models used.
*
* 2) The DATE argument is UTC expressed as an MJD. This is,
* strictly speaking, improper, because of leap seconds. However,
* as long as the delta UT and the UTC are consistent there
* are no difficulties, except during a leap second. In this
* case, the start of the 61st second of the final minute should
* begin a new MJD day and the old pre-leap delta UT should
* continue to be used. As the 61st second completes, the MJD
* should revert to the start of the day as, simultaneously,
* the delta UTC changes by one second to its post-leap new value.
*
* 3) The delta UT (UT1-UTC) is tabulated in IERS circulars and
* elsewhere. It increases by exactly one second at the end of
* each UTC leap second, introduced in order to keep delta UT
* within +/- 0.9 seconds.
*
* 4) IMPORTANT -- TAKE CARE WITH THE LONGITUDE SIGN CONVENTION.
* The longitude required by the present routine is east-positive,
* in accordance with geographical convention (and right-handed).
* In particular, note that the longitudes returned by the
* slOBS routine are west-positive, following astronomical
* usage, and must be reversed in sign before use in the present
* routine.
*
* 5) The polar coordinates XP,YP can be obtained from IERS
* circulars and equivalent publications. The maximum amplitude
* is about 0.3 arcseconds. If XP,YP values are unavailable,
* use XP=YP=0D0. See page B60 of the 1988 Astronomical Almanac
* for a definition of the two angles.
*
* 6) The height above sea level of the observing station, HM,
* can be obtained from the Astronomical Almanac (Section J
* in the 1988 edition), or via the routine slOBS. If P,
* the pressure in millibars, is available, an adequate
* estimate of HM can be obtained from the expression
*
* HM ~ -29.3D0*TSL*LOG(P/1013.25D0).
*
* where TSL is the approximate sea-level air temperature in K
* (see Astrophysical Quantities, C.W.Allen, 3rd edition,
* section 52). Similarly, if the pressure P is not known,
* it can be estimated from the height of the observing
* station, HM, as follows:
*
* P ~ 1013.25D0*EXP(-HM/(29.3D0*TSL)).
*
* Note, however, that the refraction is nearly proportional to the
* pressure and that an accurate P value is important for precise
* work.
*
* 7) Repeated, computationally-expensive, calls to slAOPA for
* times that are very close together can be avoided by calling
* slAOPA just once and then using slAOPT for the subsequent
* times. Fresh calls to slAOPA will be needed only when
* changes in the precession have grown to unacceptable levels or
* when anything affecting the refraction has changed.
*
* Called: slGEOC, slRFCO, slEQEX, slAOPT
*
* Last revision: 2 December 2005
*
* Copyright P.T.Wallace. All rights reserved.
*
* License:
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program (see SLA_CONDITIONS); if not, write to the
* Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
* Boston, MA 02110-1301 USA
*
* Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
*-
IMPLICIT NONE
DOUBLE PRECISION DATE,DUT,ELONGM,PHIM,HM,XP,YP,TDK,PMB,
: RH,WL,TLR,AOPRMS(14)
DOUBLE PRECISION slEQEX
* 2Pi
DOUBLE PRECISION D2PI
PARAMETER (D2PI=6.283185307179586476925287D0)
* Seconds of time to radians
DOUBLE PRECISION S2R
PARAMETER (S2R=7.272205216643039903848712D-5)
* Speed of light (AU per day)
DOUBLE PRECISION C
PARAMETER (C=173.14463331D0)
* Ratio between solar and sidereal time
DOUBLE PRECISION SOLSID
PARAMETER (SOLSID=1.00273790935D0)
DOUBLE PRECISION CPHIM,XT,YT,ZT,XC,YC,ZC,ELONG,PHI,UAU,VAU
* Observer's location corrected for polar motion
CPHIM = COS(PHIM)
XT = COS(ELONGM)*CPHIM
YT = SIN(ELONGM)*CPHIM
ZT = SIN(PHIM)
XC = XT-XP*ZT
YC = YT+YP*ZT
ZC = XP*XT-YP*YT+ZT
IF (XC.EQ.0D0.AND.YC.EQ.0D0) THEN
ELONG = 0D0
ELSE
ELONG = ATAN2(YC,XC)
END IF
PHI = ATAN2(ZC,SQRT(XC*XC+YC*YC))
AOPRMS(1) = PHI
AOPRMS(2) = SIN(PHI)
AOPRMS(3) = COS(PHI)
* Magnitude of the diurnal aberration vector
CALL slGEOC(PHI,HM,UAU,VAU)
AOPRMS(4) = D2PI*UAU*SOLSID/C
* Copy the refraction parameters and compute the A & B constants
AOPRMS(5) = HM
AOPRMS(6) = TDK
AOPRMS(7) = PMB
AOPRMS(8) = RH
AOPRMS(9) = WL
AOPRMS(10) = TLR
CALL slRFCO(HM,TDK,PMB,RH,WL,PHI,TLR,1D-10,
: AOPRMS(11),AOPRMS(12))
* Longitude + equation of the equinoxes + sidereal equivalent of DUT
* (ignoring change in equation of the equinoxes between UTC and TDB)
AOPRMS(13) = ELONG+slEQEX(DATE)+DUT*SOLSID*S2R
* Sidereal time
CALL slAOPT(DATE,AOPRMS)
END
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